Recently, as a non-contact automatic identification technology, radio frequency identification (RFID) has been widely used. In the RFID, non-contact data communication is performed through radio waves between an integrated circuit (IC) tag including a semiconductor memory, and a reader/writer device that reads and writes data from and to the semiconductor memory of the IC tag.
The reader/writer device in the RFID includes a communication antenna (reader/writer antenna) that radiates a radio wave towards an IC tag. As illustrated in FIG. 13, as such a communication antenna, a patch antenna including a rectangular conductor pattern 212 for radiating a radio wave on a substrate 210 made of a dielectric substance is generally used.
For example, when such a patch antenna is used to identify a position of a small IC tag having a diameter of about 40 millimeters, the patch antenna also may be downsized to correspond with the IC tag.
However, simply downsizing the patch antenna decreases the radiation power to the IC tag, making position identification of the IC tag difficult. To avoid this problem, a dielectric substance having a high dielectric-constant such as a ceramic material may be used as the substrate of the patch antenna. However, the dielectric substance such as a ceramic material is expensive, and thus the use of the dielectric substance increases the manufacture cost. A glass epoxy resin such as FR-4, which is a dielectric substance less expensive than ceramic materials, may be used as the substrate of the patch antenna, but FR-4 has a lower dielectric constant than ceramic materials. Thus the entire antenna would need to be upsized to obtain the same radiation power as a ceramic material.
To ensure sufficient radiation power to an IC tag, various types of antennas including modified conductor patterns on their substrates have been proposed. For example, an antenna including a conductor pattern having a meander-lined shape is proposed (see Published Japanese Translation of PCT International Application No. 2008-519571). The surface area of the conductor relative to the substrate is made as large as possible by forming the conductor pattern to be meandered, thereby preventing a decrease in its radiation power.
However, for this antenna, if an inexpensive substrate having a low dielectric-constant such as an FR-4 substrate is used, the length of the conductor pattern to ensure sufficient radiation power to an IC tag may be increased, thereby increasing the size in the lengthwise direction of the conductor pattern. As a result, the size of the entire antenna is increased.